A current trend in the electronics industry is a move towards lower voltage electronic devices. Over the last two decades, most TTL and CMOS devices have been designed with a five-volt operation voltage. Presently, electronic devices having a 3.3 volt operating voltage are becoming increasingly available.
Two forces have been behind moving towards the 3.3 volt devices. One force is the need for lower power devices to extend the time which an electronic circuit may be powered by a battery source. A second force has been the increasingly smaller device sizes of integrated circuits needed for higher circuit densities. Importantly, in order to increase the density of random access memories, 0.8 micron device sizes have been used, with smaller device sizes on the horizon. Smaller device technologies use a thinner gate oxide for the MOS transistors which, in turn, reduces the breakdown voltages of the device. Hence, in high density circuits, not only is a low voltage desirable, but is required for reliable operation of the devices.
One major problem in the move toward low voltage devices has been the operating frequency of the devices. As a general rule, the low-voltage devices cannot match the operating frequency of higher voltage devices. The tradeoff between operating voltage and operating frequency is particularly critical for processing devices, such as a microprocessors and microcontrollers.
Despite the advantages of low voltage devices, the market will continue to require the more standard higher voltage devices as well. Hence, it is desirable to use a design which will operate over a range of voltages rather than design two parts using different technologies, one part for low voltage operation and one part for five volt operation. For example, for a microprocessor, it would be desirable to design a part which operated from three volts to 5.5 volts, while exceeding a desired operating frequency, such as 20 MHz, at the low voltage. Consequently, the low voltage operation of the device cannot be satisfied solely by using smaller technologies, since the smaller technologies will inhibit operation at higher voltages, such as five volts.
Therefore, a need has arisen for a low-voltage, high frequency processing device which can operate reliably within a range of voltages.